A herd of hippopotamuses once owned by the late Colombian drug baron Pablo Escobar has been taking over the countryside near his former ranch - and no-one quite knows what to do with them.

It was in 2007, 14 years after Escobar's death, that people in rural Antioquia, 200 miles north-west of Bogota, began phoning the Ministry of Environment to report sightings of a peculiar animal.

"They found a creature in a river that they had never seen before, with small ears and a really big mouth," recalls Carlos Valderrama, from the charity Webconserva.

He went to look, and found himself faced with the task of explaining to startled villagers that this was an animal from Africa. A hippopotamus.

"The fishermen, they were all saying, 'How come there's a hippo here?'" he recalls. "We started asking around and of course they were all coming from Hacienda Napoles. Everything happened because of the whim of a villain."

Situated halfway between the city of Medellin and Bogota, the Colombian capital, Hacienda Napoles was the vast ranch owned by the drugs baron Pablo Escobar. In the early 1980s, after Escobar had become rich but before he had started the campaign of assassinations and bombings that was to almost tear Colombia apart, he built himself a zoo.

He smuggled in elephants, giraffes and other exotic animals, among them four hippos - three females and one male. And with a typically grand gesture, he allowed the public to wander freely around the zoo. Buses filled with schoolchildren passed under a replica of the propeller plane that carried Escobar's first US-bound shipments of cocaine.

While Don Pablo masterminded the operations of the Medellin Cartel from his villa on the hill, the locals gazed at the strange animals and even stranger concrete dinosaurs that Escobar built for his son.